Electrolyte method and composition for coloring titanium and its alloys

ABSTRACT

Titanium and titanium alloys are colored by electrolytic action to provide a colored surface of the nature of an anodized film. The colors imparted are controlled by voltage input to the electrolyte so that a wide selection of colors, each corresponding to a specific voltage level, may be obtained and reproduced from one surface to another by use of the same selected voltage levels. The electrolyte is a two-part composition consisting of an organic and an inorganic constituent. The organic constituent is one of a group of amides of which dimethylformamide is preferred. The inorganic constituent is a fluoride-bearing compound of which fluoboric acid is preferred.

United States Patent [72] Inventor Earl W. Kendall Bonita, Calif. [21]Appl. No. 732,032 [22] Filed May 27, 1968 [45] Patented Oct. 26, 1971[73] Assignee Rohr Corporation [54] IELECTROLYTE METHOD AND COMPOSITIONFOR COLORING TITANIUM AND ITS ALLOYS 19 Claims, No Drawings [52] U.S.Cl204/14 N, 204/15, 204/32 R, 204/56 R, 204/141 [51] Int. Cl C23b 5/48,C23b l/00, C23b 9/00 [50] Field of Search 204/14, 14.1, 56

[56] References Cited UNITED STATES PATENTS 2,909,470 10/1959 Schmidt204/56 2,934,480 4/1960 Slomin 204/56 3,131,134 4/1964 Micillo 204/143,257,295 6/1966 Yoezaki et al. 204/56 3 ,346,469 10/1967 Weigel 204/56FOREIGN PATENTS 895,695 5/1962 Great Britain Primary ExaminerJohn l-I.Mack Assistant ExaminerT. Tufariello AttorneyGeorge E. Pearson of thesame selected voltage levels. The electrolyte is a twopart compositionconsisting of an organic and an inorganic constituent. The organicconstituent is one of a group of amides of which dimethylformamide ispreferred. The inorganic constituent is a fluoride-bearing compound ofwhich fluoboric acid is preferred.

ELECTROLYTE METHOD AND COMPOSITION FOR COLORING TITANIUM AND ITS ALLOYSBACKGROUND OF THE INVENTION In the manufacture of aircraft it iscustomary to provide the same with a corrosion-resistant coating. Whilevarious coatings of different types have been found which are generallysatisfactory for this purpose they characteristically have added to theweight of the aircraft. With the advent of the higher speed and weightreduction requirements of present-day aircraft organic coveringmaterials as such are becoming inadequate and the need for higherstrength metals such as titanium and its alloys required. Accordingly,it is desirable to provide a coloring effect for titanium and its alloyswhich will not inherently add to the weight of aircraft parts formed inthe use of such materials, which will have no adverse effect on themechanical properties of the substrate metals, and which will provideall of the desired heat and corrosion resistant characteristics of theconventional coatings.

SUMMARY OF THE INVENTION Accordingly to the present invention titaniumand its alloys are subjected to electrolytic action to produce a coloredsurface selectively in accordance with the specific voltages applied tothe electrolyte. The colored surfaces are obtained by making thetitanium the anode in the electrolytic system, and the maximum intensityof the color is obtained after 10-60 seconds at any particular voltage.The composition of the electrolyte is nonaqueous and consists of atwo-part system of which one constituent is one of a group of amidessuch as dimethylformamide and the other constituent is a fluoridebearingcompound such as fluoboric acid.

OBJECTS OF THE INVENTION An object of the invention is to provide amethod for imparting coloring effects to titanium and its alloys throughelectrolytic action.

Another object is to impart any one of a wide variety of colors totitanium and its alloys by electrolytic action through selective controlof the applied voltage level.

Another object is to provide a method of coloring titanium and itsalloys by electrolytic action in which the time required is of the orderof less than a minute.

Still another object is to provide a method of imparting coloredsurfaces to titanium and its alloys which is of the nature of ananodized film and in which the electrolyte may be used as an immersionbath or applied by an applicator.

Yet another object is to provide a coloring of titanium and its alloysby electrolytic action of an anodizing nature in which the current flowis minimal and the current flow parameter is insignificant in relationto the voltage control parameter in producing the various color effects.

A still further object is to impart a colored surface to titanium andits alloys which is both heat and corrosion resistant.

A further object is to impart a colored surface to titanium and itsalloys by an electrolytic action of an anodizing nature which is highlyreceptive to adhesive bonding resin compositions.

Still another object is to impart a colored surface to titanium and itsalloys by electrolytic action of an anodizing nature which is effectiveto prevent the oxidation thereof under the influence of elevatedtemperatures upwards of the order of 800 F.

Still another object is to impart electrolytic coloring effects totitanium and its alloys which may readily be removed.

Yet another object resides in the provision of an electrolytic coloringprocess for titanium and its alloys which lends itself to the productionof differently colored areas on the same surface.

A still further object is to provide a coloring process as aforedescribed which lends itself to the coloring of highly polished surfacesof titanium and its alloys without impairing the efficacy of thesurfaces to control the reflectance and emissivity therefrom of radiatedenergy.

Still other objects, advantages and features of the present inventionwill become more fully apparent as the description proceeds.

MATERIALS TREATED The coloring process and electrolytic composition ofthe present invention are directed particularly to titanium, and thecoloring process is applicable to commercially pure titanium and alsoapplicable, but not limited, to the following titanium alloys upon whichthe desired surface effects have been produced by application of theprocess:

Titanium 6A 1 4V Titanium 8AllVlMo Titanium 5Al-2.5Sn

ELECTROLYTE The desired color effects are produced on the surfaces ofthe titanium and its alloys by an electrolyte action which is of ananodic nature in which the electrolyte is a nonaqueous twopartcomposition consisting of organic and inorganic materials, these beingan amide and a fluoride-bearing compound. For purposes of practicing theelectrolytic process, the electrolyte may be efiectively used eitherupon immersion therein of the articles treated or by brush applicationof the energized electrolyte to the surface of the articles treated.

The amide employed in the electrolyte may be any one of the group ofliquid amides such as dimethylformamide, dimethylacetamide,diethylformamide, formamide, diethylacetamide, t-butylformamide, andethylformamide, of which dimethylformamide is preferred for mostformulations.

The fluoride ion may be supplied from any suitable fluoridebearingcompound which is soluble in the amide such as fluoboric acid,hydrofluoric acid, fluosilicic acid, and sodium fluoborate, and othersoluble fluoride salts.

The theory of operation of the electrolytic coloring action obtainablefrom the electrolytic composition and process of the present inventionis not known. However, it is thought that the fluoride ion under theinfluence of applied voltage is responsible for color development and isprobably fortified in this effect by such ions as boron and siliconwhose presence in the electrolyte tends to make the colors morediscretely intense and vivid.

As used in the examples subsequently to be described, the composition ofthe electrolyte will generally have the following formulation:

ELECTROLYTE COM POSITION Equivalencevolumc percent Amide Fluoride Thus,the concentration of the amide is equivalent to 57-100 volume percent ofdimethylformamide as the amide in the composition, and the concentrationof the fluoride ion is equivalent to [-43 volume percent of fluobon'cacid as the fluoride-bearing compound in the composition.

As is apparent from the basic formulation, the fluoboric acid contentmay be approximately I percent of the amide content of the electrolyticcomposition without impairing the effectiveness of the electrolyte toproduce the desired surface coloring effects. 0n the other hand, thefluoboric acid content may be approximately 75 percent of the amidecontent present without producing an etchant action on the substratetitanium. Etching of a specimen of titanium 6Al-4V occurred in 10milliliters of fluoboric acid. Dimethylformamide was added until theetching ceased. The ratios of fluoboric acid to dimethylformamide was inthe order of 75 percent of the formamide, thus establishing the ratioset forth in the basic formulation. Voltage was applied anodically to aspecimen of titanium 6AI-4V immersed in 100 milliliters ofdimethylformamide and no current flow was indicated. Fluoboric acid wasadded to the 100 milliliters of dimethylformamide until a significantcoloring effect was apparent on the specimen, this occuring whenapproximately I milliliter of fluoboric acid had been added to thedimethylformamide thereby establishing the lower limit of the fluoridecontent as shown in the basic formulation. Thus, the concentration ofthe fluoride ion in the composition is equivalent to that in whichfluoboric acid comprises l-75 percent of the volume of dimethylformamideas the amide in the composition.

It is thus apparent that the amide serves two purposes in theelectrolyte, i.e., as an inert carrier for the fluoride ion and as aninhibitor to prevent attack on the substrate metal by the fluoride ion.

APPLIED VOLTAGE When titanium is made the anode in the electrolyticsystem comprising the aforedescribed electrolyte, colors are imparted tothe m'etal which are characteristic of the voltage impressed. When atitanium specimen is to be given a predetermined coior, the specimen isimmersed in the electrolyte and the required electrical connections areestablished making the titanium the anode, the cathode preferably beinga carbon electrode which need not be critically spaced relative to theanode. With the electrical connections thus established, the DC voltageis applied and increased from at a uniform rate not to exceed 2 voltsper second to the predetermined level of voltage which will produce thecolor desired. By adhering to this rate, current flow is minimized dueto an apparent electri cal resistance inherent in the colored surfaceimparted to the titanium. If the rate is exceeded, this resistanceapparently does not develop as evidenced by an increase in current flow,a lack of coloring of the surface, and in severe cases, a burningthrough of the surface.

By adding 1 weight percent of picric acid C l-IA NO OH to theelectrolyte formulation hereinabove set forth, the rate of voltage maybe increased to volts per second without encountering the currentincrease and possible burn-through conditions. The formulation with theadditive thus becomes:

ELECTROLYTE COMPOSITION (with additive) Amide I00 mls. dimethylformamideFluoride Z rnls. fluoboric acid Additive l gram picric acid Theelectrolyte may be held within a glass container since the fluoride ionis inhibited by the amide against etchant attack on the glass. In theuse of a glass container the electrolytic action in developing the colorchanges on the surface of a specimen may be observed as the voltage iselevated to the predetermined level required for the specific color tobe produced. When the voltage level is reached, continued energy flowshould be maintained for a period of from 10-60 seconds.

Different colors may be applied to different surface areas of the samespecimen. In one example, a measured volume of electrolyte was placed inthe container and a color established at the highest required voltagelevel. Subsequent to this, additional volumes of electrolyte weresuccessively placed in the container and the voltage decreased bysuccessive decrements to establish a series of different colors on thespecimen for the different levels of applied voltage. The same effectcan be produced by progressive insertion of the specimen into theelectrolyte with corresponding decreases in the level of the voltageapplied.

The applied voltage is always increased to the voltage level required toproduce a specific color desired since a color once produced cannot beremoved by lowering the voltage level. On the other hand, colorsproduced at selected voltage levels are converted to the next succeedingcolor in the spectrum when the voltage level is increased.

The surface of the titanium may be colored by the use of an applicatorsuch as a brush or roller which applies the electrolyte to the surfaceto be colored, the brush serving as the cathode in the electrolyticsystem and the different voltage levels being applied as before toproduce the different colors desired. A unique feature of the brush-onmethod of producing the colors by electrolytic action is thatdifferently coiored swaths may be laid down adjacent to each otherwithout the one adversely affecting the other. Thus, a colored swathproduced at a relatively high voltage level can be laid down adjacent toa colored swath produced at a lower level without converting the firstcolor to the second.

THE COLOR RANGE The colors produced on the surface of titanium and itsalloys are those present in the spectrum produced from white light, andthe colors produced at successively increased voltage levels appear inthe same order of colors as they are found in the spectrum. Thus, whenthe voltage is increased in increments above a level of about 10 volts,indigo, blue and green are produced in successive order which is theorder in which they occur in the spectrum. The following table of colorsand corresponding voltage levels indicates further the pattern of colorswhich are exemplary of the electrolytic process of the presentinvention.

Voltage Level Color Indigo Dark blue Light blue Green Yellow Salmon Theforegoing table is illustrative of the color range which is possible inthe use of the electrolytic method and composition of the presentinvention but is not restrictive since various other colors and shadesincluding irridescent properties are also possible.

CLEANING The specimens preferably are cleaned preparatory to producingthe colored surfaces thereon in a nonaqueous bath operated at ambienttemperature of the order of 6090 F. for about 1 to 5 minutes andconsisting of from lO-75 grams of chromic acid in lOO ml. of sulfuricacid (1.84 sp. gr.). This cleaning composition and method is the subjectmatter of US. Pat. No. 3,379,645 of Earl W. Kendall for Process andComposition for Removing Protective Paint Films. This cleaningcomposition is used for removing all forms of surface contamination oftitanium and its alloys. Such contaminants include fingerprints, grease,oil, wax, general dirt and paint coatings, In the absence of effectivecleaning to remove surface contaminants the aforementioned condition ofburnthrough is aggravated by the presence of such contaminants. Once thecolor has been produced, the titanium articles so colored may also becleaned using the same composition to remove the contaminants withoutadversely affecting the colored surface.

COLOR REMOVAL The color imparted to the surface of titanium and itsalloys in the manner as aforedescribed may be effectively removed eitherby immersion in a nonaqueous bath suitable for the purpose or by manualapplication of the bath to the colored surface to be so reate. A bathwhich is well suited for this purpose consists of 70 percent acetic acid(glacial), 20 percent sulfuric acid (L84 sp. gr.) and 10 percenthydrofluoric acid (70 percent). This bath whether used for immersion ormanual application is effectively operated at ambient temperature of theorder of 60-90 F. for about 1 to 2 minutes. This bath forms the subjectmatter of a copending application of Earl W. Kendall, Ser. No. 600,362,filed Dec. 9, 1966, for Electrolytic Descaling of Titanium and itsAlloys now U.S. Pat. No. 3,468,774

SURFACE PREPARATION FOR ADHESIVE BONDING It has been found that the peeland shear tensile strength of the adhesive bond established betweenarticles of titanium is adversely affected by the presence of oxides andother surface conditions which have not been effectively removed by theprior art cleaning process employed. It has been found that a suitablepreparation of the titanium parts to be bonded is obtained by firstcleaning the parts by immersion for about 1 to 5 minutes in a nonaqueoussulfuric acid-chromic acid composition operated at ambient temperatureof the order of 6090 F. and in which the chromic acid is in a range offrom l-75 grams per 100 ml. of sulfuric acid (L84 sp. gr.). The partsare next electrolytically cleaned for about I to minutes at a currentdensity of 4.5 to 5 amperes per square foot in a nonaqueous bathconsisting of 70 percent acetic acid (glacial), 20 percent sulfuric acid(1.84 sp. gr. and percent hydrofluroic acid (70 percent). This is thesame bath composition which is used for color removal as referred tohereinabove. The article treated is the anode in the electrolyticcleaning system which is operated in the manner set forth in theaforementioned patent application disclosing the use of the electrolyticbath. The specific color thereafter produced corresponds to a specificadhesive bonding composition which exhibits maximum adhesion to thesurface color.

SURFACE PREPARATION FOR REFLECTANCE AND EMISSIVITY OF RADIANT ENERGY Incertain applications involving the reflectance and emis sion of radiantenergy from the surfaces of titanium it is desired to impart the surfacea maximum capability with respect to reflectance and emissivity of theradiant energy. This is accomplished in accordance with the principlesof the present invention wherein the titanium article is first cleanedin the chromic acid-sulfuric acid bath aforementioned. It is thenmechanically polished to the highest degreee of reflectance possible asby well-known abrasive methods. The polished surfaces of the article arethen imparted with a color by the electrolytic process of the presentinvention with a particular color corresponding to the wave length ofthe radiant energy to be reflected SPECIFIC EXAMPLES The utility of theelectrolytic process and the composition of the present invention isillustrated in the following specific examples in which various coloredsurfaces were produced on various titanium specimens utilizing thespecific electrolyte formulations and applied voltages. In each of theexamples each of the specimens was immersed in the electrolytecomposition for a period from 10 -60 seconds at the level of voltagewhich produced the selected color for the specimen, less time beingrequired to establish the colors at the lower voltages.

EXAMPLE I Several specimens of titanium 6AI4V were connected as theanode in an electrolytic system in which the electrolyte compositionconsisted of 5 ml. fluoboric acid (HBF and 25 ml. fonnamide (HCONHQoperated at 60-90 F. with the following voltages applied to the severalspecimens to produce the colors indicated.

Voltage Level Color 20 Indigo 30 Dark blue 40 Light blue 50 Green 60Yellow Salmon EXAMPLE II Several specimens of titanium 8AllV-|Mo wereindividually made the anode in an electrolytic system in which theelectrolyte composition consisted of 70 ml. dimethylformamide and 1 ml.fluoboric acid operated at ambient temperature (6090 F.) at thefollowing voltage levels to produce the colors indicated.

Voltage Level Color Dark purple Light blue Imitation gold Lavender GreenEXAMPLE [I] A first specimen of titanium 8AllVlMo and a second specimenof titanium 6Al-4V were each cleaned in a chromic acid-sulfuric acidbath in accordance with the cleaning method aforedescribed. The titanium8Al-lV-lMo specimen was then made the anode in an electrolytic system inwhich the electrolyte composition consisted of I00 ml. dimethylformamideand 2 ml. of fluoboric acid. The cathode consisted of a rectangularsection of carbon wrapped with cheesecloth and soaked in the compositionas aforementioned. As this electrode was rubbed over one-half of thesurface of the titanium specimen, the voltage was increased at the rateof 2 volts per second until a level of 55 volts had been obtained. Thecolor applied at this voltage was yellow, The remaining surface was thenswabbed with the voltage raised from 0 to 35 volts to impart a bluecolor on the surface of the specimen.

The second specimen, titanium 6Al4V, was treated in the same manner asthe first except that the initial voltage was established at 70 volts toproduce a lavender color on one-half of the specimen and a secondvoltage was established at 50 volts to produce a green color on theremaining one-half surface of the specimen.

EXAMPLE IV Micrographs were prepared from previously colored specimensof titanium in the manner aforedescribed, and the micrographs werestudied to determine the thickness of the applied color. The micrographsdisclosed that a relatively uniform penetration of color occurred to adepth of 0.00025 inch. The depth of penetration was independent of thetime of immersion of the specimen within the electrolyte. Theelectrolytic action apparently ceases when the color is established at aselected level of voltage effective to produce that color, this beingevidenced by the apparent discontinuance of current flow as indicated byan ammeter which dropped to 0 when the color was established. Thisuniformity of penetration apparently assures maximum corrosionprotection for the substrate metal.

The resultant weight of the color film is calculated to be of the orderof 5 oz. per 10,000 square feet of the surface colored. This figure wasdetermined by cleaning the surface of aspecimen of titanium 6Al4 thedimensions of 2X2X0.032

in. and electrolytically coloring the specimen using 100 ml.dimethylformamide and 2 ml. of fluoboric acid at 40 volts for 60seconds. The difference between the initial weight and the final weightwas measured to be 0.0008 gram. This figure then was extrapolated to themore significant figure of 5 oz. per 10,000 square feet.

EXAMPLE V One specimen each of titanium 6Al4V and titanium 8Al-lV-lMowas colored blue at a 40 level in a solution consisting of 5 ml.fluoboric acid and 100 ml. of dimethylformamide. The two specimens werethen subjected to elevated temperatures of the order of 700 F. for aperiod of L hours. No change in color from the original was apparent.

EXAMPLE Vl As in example V, additional specimens prepared in the samemanner were continuously immersed in a percent sodium chloride solutionat 100 F. for 168 hoursw with no evidence of surface corrosion.

From the foregoing it is now apparent that an electrolytic method andcomposition has been provided which is well adapted to fulfill theaforestated objects of the invention. The novel principles of thisinvention transcend the scope of the invention as suggested or impliedby the several embodiments hereinbefore described, and the invention maybe embodied in other forms or carried out in other ways which have beenconceived and reduced to practice during the course of this development,without departing from the spirit or essential characteristics of theinvention. The specific examples disclosed herein therefore are to beconsidered as in all respects illustrative and not restrictive, thescope of the invention being indicated by the appended claims, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

Having thus described the invention, what is claimed as new and usefuland desired to be secured by letters patent is:

I claim:

I claim:

1. A nonaqueous electrolyte composition for anodically producingdiscrete coloring effects in relation to the level of the appliedvoltage on the surfaces of titanium and its alloys consisting of aliquid amide and a fluoride-bearing compound soluble therein, theconcentration of the amide being equivalent to 57-100 volume percent ofdimethylformamide as the amide in the composition, the concentration ofthe fluroide ion being equivalent to l 43 volume percent of fluoboricacid as the fluoride-bearing compound in the composition.

2. A composition as in claim 1 in which the amide is any one of a groupincluding dimethylformamide, dimethylacetamide, diethylformamide,formamide, diethylacetamide, t-butylformamide, and ethylformamide and inwhich the fluoride-bearing compound is any one of the group of fluoboricacid, hydrofluoric acid, fluosilicic acid, and sodium fluoborate.

3. The composition as in claim 1 in which the: amide isdimethylformamide and the fluoride-bearing compound is fluoboric acid.

4. A composition as in claim 1 in which the concentration of thefluoride ion is equivalent to that in which fluoboric acid comprisesl-75 percent of the volume of dimethylformamide as the amide in thecomposition.

5. A composition as in claim 1, including an additive, and wherein theamide constitutes 100 ml. dimethylformamide,

the fluoride compound constitutes 2 ml. hydrofluoric acid, and theadditive constitutes 1 gram of picric acid.

6. An electrolytic process for coloring the surfaces of articles oftitanium and its alloys which comprises the steps of applying voltage ofthe article to be colored as the anode in a nonaqueous electrolyticsystem in which the electrolyte consists of a liquid arnide and afluoride-bearing com ound soluble therein and in which the concentrationof e ami e is equivalent to 57-100 volume percent of dimethylformamideas the amide in the composition and the concentration of the fluorideion is equivalent to 1-43 volume percent of fluoboric acid as thefluoride-bearing compound in the composition, and increasing the voltagefrom zero to predetermined level corresponding to a specific color to beimparted to the surface of the article.

7. A process as in claim 6 in which the voltage is increased from zeroat a rate of the order not exceeding 2 volts per second.

8. A process as in claim 6 in which the predetermined voltage is appliedfor a duration of the order of l060 seconds.

9. A process as in claim 6 in which the operating temperature of theelectrolyte is of the order of 6090 F.

10. A process as in claim 6 in which the voltage is increased from zeroand in which discrete color effects are imparted at voltage levelsupwards of 10 volts.

11. The process as in claim 10 in which indigo, blue, green and yelloware exemplary of colors evidencing the spectrum and occur progressivelyin the order named as the voltage is increased in correspondingincrements to higher levels.

12. The process as in claim 6 in which the article treated is immersedin the electrolyte.

IS. The process as in claim 12 in which a carbon electrode is used asthe cathode in the electrolytic system.

14. The process as in claim 6 in which an electrolyte applicator is madethe cathode in the electrolytic system and the electrolyte is applied bythe applicator to the article to be treated.

15. The process as in claim 6 in which the article to be treated iscleaned by immersion for about I to 5 minutes in a nonaqueous sulfuricacid-chromic acid composition in which the chromic acid is in the rangeof from l075 grams per ml. of the sulfuric acid L84 sp. gr.

16. The process as in claim 6 including the further step of removing thecolor from the treated article by immersion for about 1 to 2 minutes ina nonaqueous bath consisting of 70 percent acetic acid (glacial), 20percent sulfuric acid l .84 sp. gr.) and 10 percent hydrofluoric acid(70 percent).

17. The process as in claim 16 in which the color is removed by manuallyapplying the removal bath composition to the colored surface with anapplicator.

18. The process as in claim 6 and including the additional step prior tocoloring of metallurgically polishing the surface to be colored toprovide the same with a requisite efficacy with respect to thereflectance and emissivity of radiant ener- E)- 19. The process as inclaim 15 including the further step prior to coloring ofelectrolytically cleaning the article by im mersion for about 1 to 5minutes and a current density of 455m 5 amperes per square foot in anonaqueous bath consisting of 70 percent acetic acid (glacial), 20percent sulfuric acid l .84 sp. gr.) and 10 percent hydrofluoric acid(70 percent) and in which the article treated is the anode in theelectrolytic cleaning system, the specific color thereafter producedcorresponding to a specific adhesive bonding composition which exhibitsmaximum adhesion to the surface colored.

2. A composition as in claim 1 in which the amide is any one of a groupincluding dimethylformamide, dimethylacetamide, diethylformamide,formamide, diethylacetamide, t-butylformamide, and ethylformamide and inwhich the fluoride-bearing compound is any one of the group of fluoboricacid, hydrofluoric acid, fluosilicic acid, and sodium fluoborate.
 3. Thecomposition as in claim 1 in which the amide is dimethylformamide andthe fluoride-bearing compound is fluoboric acid.
 4. A composition as inclaim 1 in which the concentration of the fluoride ion is equivalent tothat in which fluoboric acid comprises 1- 75 percent of the volume ofdimethylformamide as the amide in the composition.
 5. A composition asin claim 1, including an additive, and wherein the amide constitutes 100ml. dimethylformamide, the fluoride compound constitutes 2 ml.hydrofluoric acid, and the additive constitutes 1 gram of picric acid.6. An electrolytic process for coloring the surfaces of articles oftitanium and its alloys which comprises the steps of applying voltage ofthe article to be colored as the anode in a nonaqueous electrolyticsystem in which the electrolyte consists of a liquid amide and afluoride-bearing compound soluble therein and in which the concentrationof the amide is equivalent to 57-100 volume percent of dimethylformamideas the amide in the composition and the concentration of the fluorideion is equivalent to 1-43 volume percent of fluoboric acid as thefluoride-bearing compound in the composition, and increasing the voltagefrom zero to predetermined level corresponding to a specific color to beimparted to the surface of the article.
 7. A process as in claim 6 inwhich the voltage is increased from zero at a rate of the order notexceeding 2 volts per second.
 8. A process as in claim 6 in which thepredeterMined voltage is applied for a duration of the order of 10-60seconds.
 9. A process as in claim 6 in which the operating temperatureof the electrolyte is of the order of 60*-90* F.
 10. A process as inclaim 6 in which the voltage is increased from zero and in whichdiscrete color effects are imparted at voltage levels upwards of 10volts.
 11. The process as in claim 10 in which indigo, blue, green andyellow are exemplary of colors evidencing the spectrum and occurprogressively in the order named as the voltage is increased incorresponding increments to higher levels.
 12. The process as in claim 6in which the article treated is immersed in the electrolyte.
 13. Theprocess as in claim 12 in which a carbon electrode is used as thecathode in the electrolytic system.
 14. The process as in claim 6 inwhich an electrolyte applicator is made the cathode in the electrolyticsystem and the electrolyte is applied by the applicator to the articleto be treated.
 15. The process as in claim 6 in which the article to betreated is cleaned by immersion for about 1 to 5 minutes in a nonaqueoussulfuric acid-chromic acid composition in which the chromic acid is inthe range of from 10-75 grams per 100 ml. of the sulfuric acid (1.84 sp.gr.).
 16. The process as in claim 6 including the further step ofremoving the color from the treated article by immersion for about 1 to2 minutes in a nonaqueous bath consisting of 70 percent acetic acid(glacial), 20 percent sulfuric acid (1.84 sp. gr.) and 10 percenthydrofluoric acid (70 percent).
 17. The process as in claim 16 in whichthe color is removed by manually applying the removal bath compositionto the colored surface with an applicator.
 18. The process as in claim 6and including the additional step prior to coloring of metallurgicallypolishing the surface to be colored to provide the same with a requisiteefficacy with respect to the reflectance and emissivity of radiantenergy.
 19. The process as in claim 15 including the further step priorto coloring of electrolytically cleaning the article by immersion forabout 1 to 5 minutes and a current density of 4 1/2 to 5 amperes persquare foot in a nonaqueous bath consisting of 70 percent acetic acid(glacial), 20 percent sulfuric acid (1.84 sp. gr.) and 10 percenthydrofluoric acid (70 percent) and in which the article treated is theanode in the electrolytic cleaning system, the specific color thereafterproduced corresponding to a specific adhesive bonding composition whichexhibits maximum adhesion to the surface colored.